全文获取类型
收费全文 | 206723篇 |
免费 | 15836篇 |
国内免费 | 208篇 |
专业分类
电工技术 | 3298篇 |
综合类 | 135篇 |
化学工业 | 43404篇 |
金属工艺 | 9808篇 |
机械仪表 | 6473篇 |
建筑科学 | 4770篇 |
矿业工程 | 1889篇 |
能源动力 | 3571篇 |
轻工业 | 15749篇 |
水利工程 | 3032篇 |
石油天然气 | 8734篇 |
武器工业 | 13篇 |
无线电 | 21693篇 |
一般工业技术 | 49702篇 |
冶金工业 | 28786篇 |
原子能技术 | 6946篇 |
自动化技术 | 14764篇 |
出版年
2020年 | 2642篇 |
2019年 | 4709篇 |
2018年 | 6048篇 |
2017年 | 6474篇 |
2016年 | 7177篇 |
2015年 | 5565篇 |
2014年 | 6781篇 |
2013年 | 11298篇 |
2012年 | 7002篇 |
2011年 | 7762篇 |
2010年 | 7058篇 |
2009年 | 7463篇 |
2008年 | 7051篇 |
2007年 | 6821篇 |
2006年 | 5857篇 |
2005年 | 5240篇 |
2004年 | 5035篇 |
2003年 | 4860篇 |
2002年 | 4732篇 |
2001年 | 4593篇 |
2000年 | 4451篇 |
1999年 | 3714篇 |
1998年 | 7216篇 |
1997年 | 5298篇 |
1996年 | 3912篇 |
1995年 | 2977篇 |
1994年 | 2664篇 |
1993年 | 2774篇 |
1992年 | 2283篇 |
1991年 | 2333篇 |
1990年 | 2436篇 |
1989年 | 2351篇 |
1988年 | 2341篇 |
1987年 | 2216篇 |
1986年 | 2285篇 |
1985年 | 2322篇 |
1984年 | 2226篇 |
1983年 | 2146篇 |
1982年 | 1991篇 |
1981年 | 2207篇 |
1980年 | 2067篇 |
1979年 | 2273篇 |
1978年 | 2440篇 |
1977年 | 2443篇 |
1976年 | 3107篇 |
1975年 | 2246篇 |
1974年 | 2309篇 |
1973年 | 2347篇 |
1972年 | 2155篇 |
1971年 | 1914篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
101.
Wang Hay Kan Chenxi Wei Dongchang Chen Tao Bo Bao‐Tian Wang Yan Zhang Yangchao Tian Jun‐Sik Lee Yijin Liu Guoying Chen 《Advanced functional materials》2019,29(17)
Lithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes. 相似文献
102.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for... 相似文献
103.
Russian Engineering Research - Improvement in the wear resistance of plunger-pump rods is considered. Hardening by high-frequency current is proposed. 相似文献
104.
Changmo Kim Izhar Livne‐Bar Karsten Gronert Jeremy M. Sivak 《Molecular nutrition & food research》2020,64(4)
Lipoxins (LXs) are autacoids, specialized proresolving lipid mediators (SPMs) acting locally in a paracrine or autocrine fashion. They belong to a complex superfamily of dietary small polyunsaturated fatty acid (PUFA)–metabolites, which direct potent cellular responses to resolve inflammation and restore tissue homeostasis. Together, these SPM activities have been intensely studied in systemic inflammation and acute injury or infection, but less is known about LX signaling and activities in the central nervous system. LXs are derived from arachidonic acid, an omega‐6 PUFA. In addition to well‐established roles in systemic inflammation resolution, they have increasingly become implicated in regulating neuroinflammatory and neurodegenerative processes. In particular, chronic inflammation plays a central role in Alzheimer's disease (AD) etiology, and dysregulated LX production and activities have been reported in a variety of AD rodent models and clinical tissue samples, yet with complex and sometimes conflicting results. In addition, reduced LX production following retinal injury has been reported recently by the authors, and an intriguing direct neuronal activity promoting survival and homeostasis in retinal and cortical neurons is demonstrated. Here, the authors review and clarify this growing literature and suggest new research directions to further elaborate the role of lipoxins in neurodegeneration. 相似文献
105.
106.
E. G. Kulapina N. M. Makarova O. I. Kulapina I. A. Utc V. V. Baraguzina 《Petroleum Chemistry》2015,55(10):892-900
Potentiometric sensors with plasticized poly(vinyl chloride) membranes based on β-lactam–tetraalkylammonium ion associates sensitive to penicillin antibiotics are proposed. The physicochemical characteristics (solubility product constants and dissociation constants) of active membrane components and the electrode, transport, and selective properties of the membranes of liquidand solid-contact sensors have been studied. The quantitative characteristics of membrane transport (penetrability, ion flux, and transport rate) have been evaluated. The main charge carriers in the membranes and at the membrane/solution interface have been determined from the membrane transport characteristics. The potentiometric sensors are shown to be applicable to the determination of penicillin antibiotics in biological fluids (blood serum and oral fluid) from patients with urinary tract infection. 相似文献
107.
V. N. Oparin V. I. Vostrikov O. M. Usol’tseva P. A. Tsoi V. N. Semenov 《Journal of Mining Science》2015,51(3):624-633
The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids. 相似文献
108.
Reducing the complexity of distance measurement methods for circular turbo codes that use structured interleavers
下载免费PDF全文
![点击此处可从《International Journal of Communication Systems》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Youssouf Ould‐Cheikh‐Mouhamedou 《International Journal of Communication Systems》2015,28(9):1572-1579
The knowledge of turbo code's minimum Hamming distance (dmin) and its corresponding codeword multiplicity (Amin) is of a great importance because the error correction capability of a code is strongly tied to the values of dmin and Amin. Unfortunately, the computational complexity associated with the search for dmin and Amin can be very high, especially for a turbo code that has high dmin value. This paper introduces some useful properties of turbo codes that use structured interleavers together with circular encoding. These properties allow for a significant reduction of search space and thus reduce significantly the computational complexity associated with the determination of dmin and Amin values. © 2014 The Authors. International Journal of Communication Systems published by John Wiley & Sons, Ltd. 相似文献
109.
110.
A. A. Babenko V. I. Zhuchkov L. A. Smirnov A. V. Sychev A. A. Akberdin A. S. Kim M. F. Vitushchenko A. A. Dobromilov 《Steel in Translation》2015,45(11):883-886
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite. 相似文献